Computed tomographic evaluation of odontoid process: implications for anterior screw fixation of odontoid fractures in an adult population

Biomechanical comparison of two different compression screws for the treatment of odontoid fractures in human dens axis specimen

BACKGROUND

Lag screw osteosynthesis for odontoid fractures has a high rate of pseudoarthrosis, especially in elderly patients. Besides biomechanical properties of the different screw types, insufficient fragment compression or unnoticed screw stripping may be the main causing factors for this adverse event. The aim of the study was to compare two screws in clinical use with different design principles in terms of compression force and stability against screw stripping.

METHODS

Twelve human cadaveric C2 vertebral bodies were considered. Bone density was determined. The specimens were matched according to bone density and randomly assigned to two experimental groups. An odontoid fracture was induced, which were fixed either with a 3.5 mm standard compression screw or with a 5 mm sleeve nut screw. Both screws are certified for the treatment of odontoid fractures. The bone samples were fixed in a measuring device. The screwdriver was driven mechanically. The tests were analyzed for peak interfragmentary compression and screw-in torque with a frequency of 20 Hz.

FINDINGS

The maximum fragment compression was significantly higher with screw with sleeve nut at 346.13(SD ±72.35) N compared with classic compression screw at 162.68(SD ±114.13) N (p = 0.025). Screw stripping occurred significantly earlier in classic compression screw at 255.5(SD ±192.0)° rotation after reaching maximum compression than in screw with sleeve nut at 1005.2(SD ±341.1)° (p = 0.0039).

INTERPRETATION

Screw with sleeve nut achieves greater fragment compression and is more robust to screw stripping compared to classic compression screw. Whether the better biomechanical properties lead to a reduction of pseudoarthrosis has to be proven in clinical studies.

Radiological assessment and follow-up of a nonsurgically treated odontoid process fracture after a motor vehicle accident in Egypt: a case report

An odontoid process fracture is a serious type of cervical spine injury. This injury is categorized into three types based on the location of the fracture. Severe or even fatal neurological deficits can occur due to associated cord injury, which can result in complete quadriplegia. Computed tomography is the primary diagnostic tool, while magnetic resonance imaging is used to evaluate any associated cord injuries. These injuries can occur either directly from the injury or during transportation to the hospital if mishandled. There are two main treatment approaches: surgical fixation or external nonsurgical fixation, with various types and models of fixation devices available. In this case study, computed tomography follow-up confirmed that external fixation can yield successful results in terms of complete healing, even in cases complicated by other factors that may impede healing, such as pregnancy.

Feasibility of Two-Screw Anterior Fixation for Odontoid Fractures in a Chinese Population: A Morphometric Study Based on Computed Tomography

Background

To evaluate the feasibility of treating odontoid fractures in the Chinese population with two cortical screws based on computed tomography (CT) scans and describe a new measurement strategy to guide screw insertion in treating these fractures.

Methods

A retrospective review of cervical computed tomographic scans of 128 patients (aged 18-76 years; men, 55 [43.0%]) was performed. The minimum external transverse diameter (METD), minimum external anteroposterior diameter (MEAD), maximum screw length (MSL), and screw projection back angle (SPBA) of the odontoid process were measured on coronal and sagittal CT images.

Results

The mean values of METD and MEAD were 10.0 ± 1.1 mm and 12.0 ± 1.0 mm, respectively, in men and 9.2 ± 1.0 mm and 11.0 ± 1.0 mm, respectively, in women. Both measurements were significantly higher in men (p < 0.001). In total, 87 individuals (68%) had METD > 9.0 mm that could accommodate two 3.5-mm cortical screws. The mean MSL value and SPBA range were 34.4 ± 2.9 mm and 13.5°-24.2°, respectively, with no statistically significant difference between men and women.

Conclusions

The insertion of two 3.5-mm cortical screws was possible for anterior fixation of odontoid fractures in 87 patients (68%) in our study, and there was a statistically significant difference between men and women.

Morphometric analysis of odontoid process among Arab population: a retrospective cone beam CT study

Objective

This study aims to evaluate the feasibility of using cone beam computed tomography (CBCT) scans to assess the odontoid process diameter in the Arab population and to determine whether one or two cortical screws can be used for treating odontoid fractures.

Methods

The odontoid process of 142 individuals aged 12-75 years, including 72 males (mean age: 35.5) and 70 females (mean age: 36.2), were analyzed using CBCT scans. The sagittal and coronal CBCT views were used to evaluate the antero-posterior (AP) and transverse diameters of the odontoid process.

Results

Males had substantially bigger transverse and AP diameters of the odontoid process than females (p < 0.05 & P < 0.01 respectively). Among the sample, 97 individuals (67.4%) had external transverse diameter (METD) of less than 9 mm which is slightly bigger than that of Indians and 48 individuals (31.83%) had enough room for two 3.5 mm or two 2.7 mm screws as their METD was more than 9 mm like that of Greek and Turkish. Age had no significant impact on the morphometric measurements of the odontoid process.

Conclusion

More than sixty percent of the sample had METDs of less than 9 millimeters, indicating that a single 4.5-mm Herbert screw may be suggested for fixing fractured odontoid processes in the Arab population.

Biomechanical comparison of three different compression screws for treatment of odontoid fractures evaluation of a new screw design

BACKGROUND

Lag screw osteosynthesis in odontoid fractures shows a high rate of pseudarthrosis. Biomechanical properties may play a role with insufficient fragment compression or unnoticed screw stripping. A biomechanical comparison of different constructed lag-screws was carried out and the biomechanical properties determined.

METHODS

Two identical compression screws with different pilot holes (1.25 and 2.5 mm), a double-threaded screw and one sleeve-nut-screw were tested on artificial bone (Sawbone, densities 10-30pcf). Fragment compression and torque were continuously measured using thin-film force sensors (Flexiforce A201, Tekscan) and torque sensors (PCE-TM 80, PCE GmbH).

FINDINGS

The lowest compression reached the double-threaded screw. Compression and sleeve-nut-screw achieved 214-298% and 325-546%, respectively, of the compression force of double-threaded-screw, depending on the test material. The pilot hole optimization led to a significant improvement in compression only in the densest test material. Screw stripping took place significantly later with increasing density of the test material on all screws. In compression screws this was done at a screw rotation of 180-270°, in sleeve nut screw at 270-720° and in double-threaded screws at 300-600° after reaching the maximum compression.

INTERPRETATION

Double-threaded screw is robust against screw stripping, but achieves only low fragment compression. The classic compression screws achieve better compression, but are sensitive to screw stripping. Sleeve-nut screw is superior in compression and as robust as double-threaded screw against screw stripping. Whether the better biomechanical properties lead to a reduction in pseudarthrosis must be proven in clinical trials.

Computerized Tomography-Based Morphometric Analysis of Odontoid in 100 Egyptian Patients

Background

There is still no consensus in the literature regarding the use of 1 screw or 2 screws. A number of studies have proved ethnic variations in the morphometry of the odontoid. There is no literature on the morphometry of odontoid in Egyptian patients.

Methods

Computerized tomography (CT) scans of the head and cervical spine of 100 healthy (no evidence of cervical spine fracture) patients of Egyptian origin were studied. Measurements were performed using Horos software, which allowed exact morphometric measurements to be taken at a specific angle in the axial, coronal, and sagittal planes.

Results

The mean age was 48.57 ± 15.39 years (range, 18-79 years; 56 male and 44 female patients). The mean radiologically calculated screw length and the mean radiologically calculated screw insertion angle were 38.21 ± 2.2 mm and 55.7° ± 3.84°, respectively. The mean anteroposterior and transverse diameter of the odontoid at the waist in the axial cut were 11.02 ± 1.05 mm and 8.92 ± 0.93 mm, respectively. A total of 54% and 6% of the study sample had the transverse waist diameter of the odontoid in the axial cut below 9 mm and 7.4 mm, respectively. A total of 48% of the male and 61% of the female patients had their transverse diameter of the odontoid at the waist below 9 mm. There was a statistically significant difference in all the measurements of the odontoid between the male and female patients except in the anteroposterior diameter of the base of odontoid (P = .06) in the axial cut, and the radiologically calculated screw insertion angle (P = .57). The mean distance between the apex of the odontoid and the screw exit was 1.8 ± 0.75 mm (range, 0-3 mm).

Conclusions

CT-based morphometric analysis of the odontoid is necessary before using 2-screw fixation technique. Single 4.5-mm Herbert screws could be used in all Egyptian patients without the need for CT-based morphometric analysis of the odontoid. The posterior screw can violate the posterior wall of the odontoid, with a reduced fracture hold and a chance of injuring the thecal sac.

The Y-shaped trabecular bone structure in the odontoid process of the axis: a CT scan study in 54 healthy subjects and biomechanical considerations

OBJECTIVE

Odontoid process fractures are very common in both young and geriatric patients. The axial trabecular architecture of the dens appears to be crucial for physiological and biomechanical function of the C1-2 joint. The aim of this study is to demonstrate the presence of a Y-shaped trabecular structure of the dens on axial CT and to describe its anatomical and biomechanical implications.

METHODS

Fifty-four C2 odontoid processes in healthy subjects were prospectively examined for the presence of a Y-shaped trabecular structure at the odontocentral synchondrosis level with a dental cone beam CT scan. Length, width, and axial area of the odontoid process were measured in all subjects. In addition, measurements of the one-third right anterior area of the Y-shaped structure were taken.

RESULTS

The Y-shaped trabecular structure was found in 79.6% of cases. Length and width of the odontoid process were 13.5 ± 0.6 mm and 11.2 ± 0.9 mm, respectively. The mean area of the odontoid process at the odontocentral synchondrosis was 93.5 ± 4.3 mm2, whereas the mean one-third right anterior area of the odontoid process at the same level was 29.3 ± 2.5 mm2. The mean area of the odontoid process and its length and width were similar in men and women (p > 0.05). No significant difference was found in the mean area of the odontoid process in people older than 65 years (94 ± 4.2 mm2) compared to people younger than 65 years (93.3 ± 4.4 mm2; p > 0.05).

CONCLUSIONS

The authors identified a new anatomical entity, named the Y-shaped trabecular structure of the odontoid process, on axial CT scans. This structure appears to be the result of bone transformation induced by the elevated dynamic loading at the C1-2 level. The presence of the Y-shaped structure provides new insights into biomechanical responses of C2 under physiological loading and traumatic conditions.

Morphometric Evaluation of Craniocervical Junction by Magnetic Resonance Imaging Method

Purpose:

Morphometric evaluation of the craniocervical region using magnetic resonance imaging method in humans and determination of the reference values that could be used in various clinics were the aims of this study.

Materials and Methods:

In our study, 306 (95 males and 211 females) individuals who met the necessary criteria for anatomical structure were included and taken measurements afterward. Sagittal T1- and T2-weighted images were determined as a section thickness of 3 mm, an interval of 10 mm, a matrix of 352 × 224, a field of view of 170–240 mm, and a number of excitations of 4. Measurements of anatomical structures in the craniocervical region were taken via these images.

Results:

Statistically significant differences were found among the findings of male and female individuals such as height of dens axis, anteroposterior distance of the dens axis (APDDA), anterosuperior distance of the dens axis (ASDDA), sagittal diameter of the foramen magnum (SDFM), total cervical vertebra length (TCVL), distance of spatium retropharyngeum, Pavlov ratio, and the ratio between sagittal diameter of canalis vertebralis (SDCV) to the APDDA. Dens axis height showed a positive correlation with ASDDA and TCVL, and a negative correlation was found between the APDDA and the spatium retropharyngeum.

Conclusion:

Age- and sex-related changes in the measurements of anatomical regions reveal that an increase and a decrease in the various parameters reveal that these are the normal changes presumably determined by the functional and physical demands varying on the columna vertebralis.

Feasibility of Modified Anterior Odontoid Screw Fixation: Analysis of a New Trajectory Using 3-Dimensional Simulation Software

BACKGROUND

Anterior odontoid screw fixation (AOSF) has been suggested as the optimal treatment for type II and some shallow type III odontoid fractures. However, only the classical surgical trajectory is available; no newer entry points or trajectories have been reported.

METHODS

We evaluated the anatomic feasibility of a new trajectory for AOSF using 3-dimensional (3D) screw insertion simulation software (Mimics). Computed tomography (CT) scans of patients (65 males and 59 females) with normal cervical structures were obtained consecutively, and the axes were reconstructed in 3 dimensions by Mimics software. Then simulated operations were performed using 2 new entry points below the superior articular process using bilateral screws of different diameters (group 1: 4 mm and 4 mm; group 2: 4 mm and 3.5 mm; group 3: 3.5 mm and 3.5 mm). The success rates and the required screw lengths were recorded and analyzed.

RESULTS

The success rates were 79.03% for group 1, 95.16% for group 2, and 98.39% for group 3. The success rates for groups 2 and 3 did not differ significantly, and both were significantly better than the rate for group 1. The success rate was much higher in males than in females in group 1, but the success rate was similar in males and females in the other 2 groups. Screw lengths did not differ significantly among the 3 groups, but an effect of sex was apparent.

CONCLUSIONS

Our modified trajectory is anatomically feasible for fixation of anterior odontoid fractures, but further anatomic experiments and clinical research are needed.

Anterior fixation of odontoid fractures: results

Objective

To evaluate the clinical and radiological outcomes of the surgical treatment in patients diagnosed with odontoid fracture who underwent open reduction and internal fixation (ORIF) with screws.

Methods

This was a retrospective study with nine patients. Pain (visual analog scale [VAS]) and neurological status (Frankel scale) were assessed. The neck disability index (NDI) and the post-operative cervical range of motion were calculated. The cervical spine was radiologically evaluated (X-ray and CT) pre- and postoperatively.

Results

The mean age of patients was 70 years. All patients presented type IIb (Grauer classification) fractures, with a mean deviation of 2.95 mm. Two patients had subaxial lesions. The mean follow-up was 30 months. The mean time from trauma to surgery was seven days. The pre-operative Frankel score was E in all except one patient (B), in whom a post-operative improvement from B to D was observed. Post-operative pain was 2/10 (VAS). A total of 77% of patients presented a mild or moderate disability (NDI). Six patients regained full range of cervical movement, and bone union required approximately 14 weeks. Pseudarthrosis complications were observed in two patients (77% union rate), one patient presented screw repositioning and one case, dysphonia.

Conclusion

Delayed diagnosis is still an issue in the treatment of odontoid fractures, especially in elderly patients. Concomitant lesions, especially in younger patients, are not uncommon. The literature presents high fusion rates with ORIF (≥80%), which was also observed in the present study. However, surgical success depends on proper patient selection and strict knowledge of the technique. This pathology presents a reserved functional prognosis in the medium-term, especially in the elderly.

Computational anatomy of the dens axis evaluated by quantitative computed tomography: Implications for anterior screw fixation

The surgical fracture fixation of the odontoid process (dens) of the second cervical vertebra (C2/axis) is a challenging procedure, particularly in elderly patients affected by bone loss, and includes screw positioning close to vital structures. The aim of this study was to provide an extended anatomical knowledge of C2, the bone mass distribution and bone loss, and to understand the implications for anterior screw fixation. One hundred and twenty standard clinical quantitative computed tomography (QCT) scans of the intact cervical spine from 60 female and 60 male European patients, aged 18-90 years, were used to compute a three-dimensional statistical model and an averaged bone mass model of C2. Shape and size variability was assessed via principal component analysis (PCA), bone mass distribution by thresholding and via virtual core drilling, and the screw placement via virtual positioning of screw templates. Principal component analysis (PCA) revealed a highly variable anatomy of the dens with size as the predominant variation according to the first principal component (PC) whereas shape changes were primarily described by the remaining PCs. The bone mass distribution demonstrated a characteristic 3D pattern, and remained unchanged in the presence of bone loss. Virtual screw positioning of two 3.5 mm dens screws with a 1 mm safety zone was possible in 81.7% in a standard, parallel position and in additional 15.8% in a twisted position. The approach permitted a more detailed anatomical assessment of the dens axis. Combined with a preoperative QCT it may further improve the diagnostic procedure of odontoid fractures. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2154-2163, 2017.

Cervical pedicle morphometry in a Latin American population: A Brazilian study

The goal of this study was to conduct a detailed computed tomography (CT) assessment in the Brazilian population of the screw starting point, trajectory, and dimensions of pedicle in the cervical spine.Two hundred consecutive patients were retrospectively evaluated using cervical spine CT, with imaging reconstruction of each cervical vertebrae in the axial plane with 2 mm, and in sagittal reconstructions with 3 mm. Parameters in axial plane included the pedicle width (PW), pedicle axis length (PAL), pedicle transverse angle (PTA), and the distance from the entry point to the point between the lamina and spinous process (DEP). Measurements in the sagittal plane involved the pedicle height (PH) and the pedicle sagittal angle (PSA).The mean PW and PH were smaller in females than in males in all cervical vertebrae, but there were no significant differences of PTA among genders. PSA ranged from 15.2° to 23.7°. Mean values of PAL and DEP had a tendency to decrease from the proximal to distal cervical vertebrae. PW was <4 mm in 7.5% of men (C3) and 25% of women (C3), and <4.5 mm in 20% (C3 male) and 66% (C3 female). The intra- and inter-observer reliability were very good for the tomographic measurement of PW, and good for PH. For PAL, the intraobserver reliability was good, but the interobserver reliability varied from moderate to good. Considering PTA and PSA, the intraobserver reliability was good, but the interobserver reliability moderate for PTA and poor or fair for PSA. DEP measurements showed poor intraobserver reliability, and poor or moderate interobserver reliability.Our results presented similar trend of previous studies, but the frequency of patients with PW <4.5 mm in our population is higher, suggesting an increased risk during the attempting of transpedicular screw technique.

The Feasibility of Two Screws Anterior Fixation for Type II Odontoid Fracture Among Arabs

STUDY DESIGN

Retrospective, cross-sectional study.

OBJECTIVE

To evaluate the feasibility of two screws anterior fixation of the odontoid process among Arab adults.

SUMMARY OF BACKGROUND DATA

Anterior screw fixation is the treatment of choice for type II odontoid fractures. In order to perform the procedure safely, the diameter of the odontoid process should be wide enough to allow for the placement of one or two screws.

METHODS

A retrospective review of 156 computed tomography scans of the cervical spine was done. The included patients were Arabs, adults (at least 18 years old), and had no evidence of upper cervical spine trauma, deformity, infection, tumor, or surgery. The minimum external transverse diameter (METD), minimum internal transverse diameter (MITD), minimum external anteroposterior diameter (MEAD), and minimum internal anteroposterior diameter (MIAD) of the odontoid process were measured. A P value of ≤0.05 was considered as the cutoff level of statistical significance.

RESULTS

Our study included 94 (60.3%) males and 62 (39.7%) females. The mean age of the subjects was 37.8 ± 16.9 years (range 18-85). The mean values of the METD, MITD, MEAD, and MIAD were 8.7 ± 1.0 mm, 6.0 ± 1.1 mm, 10.3 ± 1.0 mm, and 7.4 ± 1.1 mm, respectively. Men had larger diameters compared to women. This was statistically significant for METD (P = 0.035) and MEAD (P < 0.001). The METD was <9.0 mm in 95 (60.9%) subjects, while the MITD was <8.0 mm in 153 (98.1%) subjects. These findings were not significantly different between males and females.

CONCLUSION

Two screws anterior fixation of type II odontoid fracture is not feasible among the majority of Arabs.

LEVEL OF EVIDENCE

3.

Morphometric analysis of the odontoid process: using computed tomography--in the Greek population

AIM

A morphometric analysis of the odontoid process of the A2 vertebra, in the Greek population, was conducted using CT scan. We aimed to determine the feasibility to use one or two screws when treating fractures of this anatomic element.

PATIENTS AND METHODS

One hundred and fifteen patients (57 men) of a mean age of 48 years (16-95 years) underwent a cervical spine CT scan examination. The anterior-posterior and transverse diameters of the odontoid process were measured from the base, at 1-mm interval upward on axial CT images. The length from the tip of the odontoid process to the anterior-inferior angle of the body of the axis was calculated. Data concerning the height and weight of the examined patients were collected.

RESULTS

The mean transverse and anterior-posterior distances were found to be 11.46 and 10.45 mm, respectively, for the upper end of the odontoid process. At the neck level of the odontoid process, the equivalent mean values were 11.12 and 8.73 mm, respectively, while at the base, these distances were found to be 13.84 and 12.3 mm, respectively. The mean distance from the tip of the odontoid to its base was 17.25 and 17.28 mm, respectively, while the mean distance from the tip of the dens to the anterior-inferior corner of the axis' body was 39.2 mm. Men showed greater values than women.

CONCLUSIONS

In this study, it was shown that in the Greek population there is enough room for one 4.5-mm or one 3.5-mm cannulated screw to be used. The application of two 3.5-mm screws is feasible in 58.6 % of the male and 26.3 % of the female population. This confirms that the knowledge of the true dimensions of the odontoid process is of paramount importance before the proper management of fractured dens using the anterior screw technique.

ONE OR TWO SCREWS IN THE FRACTURE OF THE ODONTOID PROCESS? EVALUATION USING COMPUTED TOMOGRAPHY

Objective:To evaluate the bone area of the odontoid process through computed tomography and its relation with the area of one and two screws in the male and female subjects.Methods:188 CT scans of adults were analyzed. The isthmus area was selected and the transverse diameter was measured at 1.2 mm from the base of odontoid.Results:After placement of a screw, the odontoid area remains with 82% of free bone for both men and women. With two screws, 45.6% of women, had a free bone area of the odontoid process between 50% and 75% and 54.4% were above 75%. 26.6% men had percentage from 50% to 75% of free bone area and 73.4% above 75% (p=0.07). After the placement of two screws, the bone area was, in average, 77.3% in men and 75.4% in women. Using the Student t-test, the differences between the average of percentage of free bone area in men and women are significantly lower in women (p=0.0012).Conclusion:The pre-operative planning through CT can help to choose the number of screws in the odontoid process. The choice should be particularly careful when using two screws in women.

The three-dimensional morphometry of the odontoid peg and its impact on ventral screw osteosynthesis

Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis. Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability. The mean length of the odontoid peg was 39.76 mm (SD 2.68). The mean screw entry angle α was 59.45° (SD 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (SD 2.70), the maximum possible mean converging angle of two screws was 20.35° (SD 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (SD 0.84) for the inner diameter in the sagittal plane and 7.35 mm (SD 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (SD 0.91) in the sagittal plane and 11.77 mm (SD 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (SD 1.14) for the sagittal inner diameter and 5.50 mm (SD 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (SD 1.0) in the sagittal plane and 10.00 mm (SD 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible. The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws.

CT based evaluation of odontoid morphology in the Indian population

BACKGROUND

Anterior fixation using two 3.5 mm screws is typically recommended for type II odontoid fractures. However, it is unsuitable in patients with an odontoid diameter of <9.0 mm. There is no data regarding the morphology of odontoid process in the Indian population. The aim of our study was to: a) Measure the external diameters of odontoid process in the Indian population using CT scan and thus determine the feasibility of two 3.5 mm screw fixation in them. b) Determine if any correlation exists between body height (Ht) and weight (Wt) and external odontoid diameters.

MATERIALS AND METHODS

CT images of odontoid process of 100 consecutive patients were analyzed. Antero- posterior (AP) and transverse (TD), outer diameters of the odontoid process were measured from the base and at 1 mm interval upwards on axial CT images.

RESULTS

The mean AP and mean TD were 11.52 mm and 9.85 mm, respectively. Fifty-five (55%) of the patients had at least one TD <9.0 mm. Five (5%) patients had at least one TD <7.4 mm. None of the patients had any diameter <5.5 mm. Body Ht correlated significantly with mean AP and mean TD of the odontoid process (AP: r = 0.276, P = 0.013; TD: r = 0.359, P = 0.001), whereas body Wt correlated significantly only with mean TD (AP: r = 0.162, P = 0.15; TD: r = 0.297, P = 0.007).

CONCLUSION

More than half of the study population (55%) was unsuitable for two 3.5 mm screw fixation for type II odontoid fracture. Two 2.7 mm screws can be safely used in 95% of the population. A 4.5 mm Herbert screw can be safely used in the entire population. We recommend two 2.7 mm screws or a 4.5 mm Herbert screw for fixation of these fractures in the Indian population. Body height showed a significant correlation with external odontoid diameters, whereas weight showed significant correlation only with TD of the odontoid process.